Effects of Perinatal Progesterone on Mouse Mammary Differentiation In Vitro: Brief Communication 2 3

Abstract

The effects of perinatal injection of progesterone on hormone sensitivity of mammary glands to the induction of lobules were investigated after in vivo pretreatment and subsequent organ culture. The mammary tissues of C57BL/Crgl mice given injections of 100 μg progesterone on each of the first 5 days of life and those of un inoculated controls were organ cultured on week 4 of life after 4, 6, or 9 days of pretreatment injections (1 μg 17β-estradiol plus 1 mg progesterone). The effects of several hormone supplements to the chemically defined culture medium were assessed. Lobular development was similar in tissues of mice given injections of progesterone perinatally and their controls after in vivo pretreatment; after culture with 17β-estradiol, progesterone, aldosterone, growth hormone, prolactin, insulin, and thyroxine; or after culture with insulin and thyroxine. Lobular development was enhanced after 6 but not after 9 days of pretreatment followed by culture with 17β-estradiol, progesterone, aldosterone, insulin, and thyroxine. Alveolar but not lobular development was enhanced in tissues from mice given injections of progesterone perinatally after 9 days of pretreatment followed by culture with insulin and thyroxine. Perinatal injection of progesterone, a treatment previously reported to promote mammary tumorigenesis in mice, did not uniformly influence in vitro lobular differentiation of their mammary glands. These results are in contrast to our previous finding that perinatal injection of estrogen in mice, a treatment that is also tumorigenic in the mammary glands, does increase in vitro lobular differentiation in response to mammotropic hormones. Life events subsequent to neonatal exposure may be necessary to promote the expression of tumorigenic potential in the mammary tissues of mice given injections of progesterone neonatally.